texts: How to determine the age of a star using asteroseismology?

texts:
I keep reading that a standard way to determine the age of a star is asteroseismology, and I tried to learn more about it. I am wondering if somebody could help me to describe the method in simple terms for a primary school kid. That should be easier for experts of that field.
I found a review article Asteroseismology of High-Mass Stars: New Insights of Stellar Interiors With Space Telescopes a good starting point for myself, but that is not yet at the layperson level I am aiming for:

The study of stellar structure and evolution using stellar oscillations—asteroseismology—has undergone a revolution in the last two decades thanks to high-precision time series photometry from space telescopes. In particular, the long-term light curves provided by the MOST, CoRoT, BRITE, Kepler/K2, and TESS missions provided invaluable data sets in terms of photometric precision, duration and frequency resolution to successfully apply asteroseismology to massive stars and probe their interior physics. The observation and subsequent modeling of stellar pulsations in massive stars has revealed key missing ingredients in stellar structure and evolution models of these stars.

My question in other words: What observation variables does one need from a star in order to calculate the age using asteroseismology? Following what recipe will bring me from the observations to a number for the age? What accuracies are possible?
Related

Wikipedia on Stellar Age Estimation
Can someone calculate the age of the KOI-4878 star?


texts: If I travelled near a black hole, my time would progress slower relative to someone on Earth. This is clear enough. However, what if we sent a probe with a camera to a black hole? When we watch the screen, would we see time through the camera's perspective — that is, would the Universe appear to progress faster as the probe got closer and closer to the black hole?


texts: Do all galaxies have a black hole in the center?

texts:
Would I be correct if I stated that all galaxies have a black hole in the center? Since other galaxies orbit around a center point in a galaxy - the barycenter, right? - I would assume at this point there must be some insane gravitational pull. Which only black holes can create, right?

(If this is a bit vague, please tell me so I can clarify!)
I am a complete newbie to astronomy in general, so sorry if this question makes no sense whatsoever.


texts: Why do objects all orbit in the same direction?

texts:
In a solar system or a planet that has many moons, why do their orbiting objects all orbit in the same direction?

Is it possible for two orbiting masses to orbit in the opposite direction of each other?


texts: How to calculate how much a galaxy moves from its coordinate at redshift 0 to redshift 1?

texts:
I have two simulation snapshots in my hand at redshift 0 and 1. I know x, y, z coordinates of the galaxies in both redshifts 0 and 1, however there is no way for me to identify a single galaxy in both redshifts, i.e., there is no tracker/tracer for the galaxies that will trace the position of galaxies from redshift 1 to 0.

Now I have halo catalogue for both $z =0$ and $z=1$ and I am interested to trace a certain galaxy from z=0 to 1. I know that galaxy's exact x,y,z at $z =0$. My initial plan is to create a search with $\sqrt{x^2+y^2+z^2}\le r$ in kpc. So any galaxy at redshift 1 with coordinates less than r maybe a potential candidate.

My question is, is there any intelligible guess of what a potential value of r would be in kpc? In other words, I am interested to know with reduced Hubble parameter $h = 0.7$, how much far a galaxy might move from $z = 1$ to $z =0$?


texts: Does the magnetic field of earth restore?

texts:
The magnetic field of earth protects us from solar wind as we know it, but after the solar wind interacts our magnetic field.

Does the magnetic field of earth restore after it deflects the solar wind from the sun?


texts: How long between the moment a meteor is first visible and the moment a meteorite hits the ground?

texts:
A meteor is usually only visible for a couple seconds at most, but I would guess that it usually stops being visible high above the ground.
Meteors often don't make it to the ground as they completely burn up before. But among those that do reach the ground, how long does it take for a meteoroid to go through the Earth's atmosphere and hit the ground? How many seconds between the moment it is first visible and the moment it hits the ground?


texts: Did comets 266P/Christensen or P/2008 Y2 (Gibbs) cause the Wow! signal?

texts:
Continuing my fascination with the Wow! signal, I stumbled upon an article from 2016 titled Famous Wow! signal might have been from comets, not aliens.

It describes the hypothesis that the signal might have been generated by an (at the time) unknown comet. Quoting from the article:

  Antonio Paris […] thinks the signal might have come from one or more passing comets. He points the finger at two suspects, called 266P/Christensen and P/2008 Y2 (Gibbs).

…and:

  To test his idea, Paris proposes looking at the same region of space when the comets are back. Comet 266P/Christensen will transit the region first, on 25 January 2017, then P/2008 Y2 (Gibbs), on 7 January 2018. An analysis of the hydrogen signal of the comets should reveal if he is correct.

(emphasis mine)

It has now been two years since these comets came back, and I would be surprised if this hypothesis was not tested. Assuming it was tested, what were the results?


texts: Should a station in orbit around the Sun travel in the same or the opposite direction to the planets?

texts:
If we put a station in orbit around the Sun, and wanted to send transports as regularly as possible without the travel costs being prohibiting; should we have it rotate around the Sun clockwise, or anti-clockwise like the other planets?

(I'll be checking the page frequently so feel free to post comments and questions should you have them. I'll respond as quickly as possible.)


texts: How should I think about sunlight for the purposes of analyzing the angles it makes w/ earth?

texts:
Most diagrams I see of sunlight look like something like this:

.

They show that for basic geometric analyses, the sun's radiation can be thought of as 'thin lines' that strike earth. Further, at an equinox, those rays strike hit the horizon of every point on earth (except the poles) directly from the east. So, the diameter for the earth does not matter at all it terms of the angle at which the rays strike.

I'm curious - how far will this conceptual frame take me? What is a better way to conceptualize how the sun's light strikes the earth?


texts: Why does mass naturally move closer toward's the center of other masses?

texts: If general relativity is understood to mean that mass curves space such that objects are still traveling in a straight line, why does mass naturally move closer toward's the center of other masses?


texts:
In a paper called Further Observational Evidence for a Critical Ionising Luminosityin Active Galaxies, Section 2.1, the authors talk about using the ICRF2 to find a tuning frequency in search of the 21-cm absorption (of HI):

The Second Realization of the International Celestial Reference Frame by Very Long Baseline Interferometry (ICRF2, Ma et al.2009), constitutes a sample of strong flat spectrum radio sources,of which 1682 now have known redshifts (Titov & Malkin 2009; Titov et al. 2013 and references therein), yielding a tuning frequency in the search for 21-cm absorption. Being VLBI sources, all have significant compact flux, thus maximising the chance of a high covering factor and thus optical depth (Curran et al. 2013a).The original aim of the survey was to form part of a large observing campaign to search and quantify the incidence of associated ${\rm H\,{\small I}\,21}$-cm absorption over all redshifts, although observing time was only granted for the high redshift $(z \gtrsim 2.6)$  proposals.

Since we already know the frequency of HI (1420.40575177 MHz), why is this so important? What am I missing about the functioning of radio telescopes?
This question doesn't really answer my query.


texts: Estimating upper limits on flux values (Radio)

texts: How to estimate upper limits on flux values for a radio source if it is not seen in NVSS (1.4 GHz survey) but is observed in lower radio frequency maps?


texts: The specifics of two Earth-like worlds orbiting each other?

texts:
I'm currently looking into writing a story or two set on twin worlds, which I came to find out in my research is apparently not a new idea (Double planets?
 Rocheworlds?  Am I close?).  But I want it to be as scientifically plausible as possible, so I'm here fact-checking.  I guess my main question going forward is: is the description of my worlds, as they are, scientifically plausible, and if not, what should I change?

Specifically, these two worlds are very similar to our own Earth.  To simplify things, let's say they have the exact same or relatively similar atmosphere and living conditions, so that humans and Earth-based life can live on it without much or noticeable acclimation.  If you were to hop a ship from Earth and landed on one or the other, getting off the ship you would notice little to no difference than you would on Earth.  Similarly, the short trip between each world shows little to no difference, although one has slightly more gravity than the other.

The only real difference between the two worlds themselves is that one is slightly smaller than the other, but by an almost negligible amount (a few thousand miles); the difference isn't as dramatic as, say, Earth and Mars orbiting each other, maybe Earth and Venus being the better comparison.
Let's also suppose that they are also far enough away from one another that they aren't dramatically effecting one another's gravity or tides, etc., but are still visible in one another's skies, prominent enough to be important to the culture of the other.  I initially wanted them to be very prominent in one another's skies, but I suppose being as close as the moon is to our world would be too close: I'm curious as to how far away one would have to be and still be caught in the other's gravity (I suppose the smaller of the two would have to be the one caught in the bigger one's gravity?  I plead ignorance on that one).

I'm in love with the idea that they broke off from one another in the same way the Earth and the moon supposedly did billions of years ago, in an impact event, and they slowly came to orbit one another (although this idea has recently been challenged, is my understanding).  From what I've read, though, it might be more plausible that one formed naturally in the disk formation of that planet's solar system, and a rogue planet got caught in its gravitational pull.  I like that idea less, but I'm not so proud I can't just get over it.

In my head, they have their own day and night cycles, just like Earth.  They may not have identical hours in a day or days in a year, etc., but its similar.  They same face of the planet is never quite facing the face of the other: it's not like the moon, which is locked to one side always facing us and the other always away.  From what I've researched, though, it's probably more likely that the planets would be facing one another on one side constantly, and their day-night systems would be greatly affected by that.  Again, not in love with that idea, but if it has to go, it has to go.

That's all I have for now.  I would try to explain how they rotate one another better, but I can't: I'm terrible in that area, and I've forgotten a lot of the terms you use in describing this.  Please let me know what your thoughts are.


texts: Do the orbits of planets change? Where is the data for this?

texts:
Everything in the space is moving all the time.
Do the orbit of major Solar Systems planets, Mercury to Saturn change? Just like Moon's orbit around Earth changes.
How often, how small or big is the change?
Where can I find data on this?


texts: How is the magnitude of a star measured?

texts: How does one measure the brightness of a star?, I did not find anything on the internet.


texts: My telescope is blurry and I am not sure why I used a 254mm primary mirror f/5 with a secondary mirror at 62.5 and I also used a 32mm eye piece I know if I stand back 20cm from eyepiece I see a clear image but any closer and it gets blurry can someone tell me what I am missing


texts:
According to Newton, gravity is the pulling - or in fact the attracting - force of any heavenly body towards any object to its center. But, to the contrary, Einstein once said that the four dimensions of space and time push the object downwards.

So can which one of them is correct?


texts: Has the great Andromeda Galaxy ever collided with any galaxies?

texts:
We know that the Andromeda Galaxy is moving towards the Milky Way and vice versa, so there will be a collision. Because of the vast space between them, the  stars as they are defined will not themselves come into contact until much later if at any time at all.

My question is whether Andromeda has had a collision prior to this 4 billion year inevitability.


texts: Which celestial object in the solar system has the fastest tangential velocity at its surface?

texts:
Consider all of the naturally-occurring objects in the solar system : in the reference frame of the object's center (ie, ignoring the orbital velocity around the sun or, in the case of satellites, their planet) and considering an average point on their surface : which object has the fastest tangential velocity?

Note - I am not asking about the rotational velocity ($\omega$), but the tangential velocity, which for a solid spherical body would be simply $\vec v=\vec \omega\times r $. Since the solar system is typically not made of up homogeneous solid spheres, I can't just look up the tables of rotational velocities and radii of the objects.

I'm looking to be surprised, so everything goes : planets, their satellites and any of the other known objects (comets, asteroids, etc) - the only condition should be that this velocity should be more or less constant (I'm not sure if bodies in highly-elliptical orbits have severe changes in rotational velocity as they approach the sun).


texts: MeerKAT's Epic Image of the Galactic Centre, what are we seeing?

texts:
In this answer as well as this one, I've linked to New Jersey Institute of Technology's Dr. Dale Gary's nicely-written Physics 728 Radio Astronomy; Lecture #1 notes where I can see the image below. It links to Gizmodo.au's New South African Telescope Releases Epic Image Of The Galactic Centre.

I have heard of the Meerkat array earlier (Which 16 antenna locations are used for the MeerKAT radio image recently announced?), but I am wondering how to read further about this spectacular image. What is the scale for example? How would it look pasted into the arc of the Milky Way; just a tiny patch of a few arc-minutes, or several tens of degrees?

How will this compare to the radio image of Sag A* that we will see in the next day or two?

Also, if anyone knows, what are those spiky arcs sticking up, and those puff-ball things on the left?

Source: Gizmodo "The black hole at the centre of the Milky Way and filaments." Credit: SARAO, click for full size.


texts: What is the opposite of the vernal point?

texts: The equator and the ecliptic cross at two nodes. One of those nodes is the vernal point. What is the other one called?


texts: Does the sun have cycles causing temperature changes on Earth?

texts:
Can the Sun go through seasons or cycles to cause a temperature change?

Could the Sun have to go through any kind of thermal cycle to change the climate on Earth and by how much?


texts: Why do dark objects look white from a distance? (Moon, Ceres, but not Earth!)

texts:
What makes the Moon shine white in the sky, although it seems to be as dark as asphalt?

Earth's average albedo is 3 and 4 times that of the Moon and Ceres respectively (0.37 vs 0.12 and 0.09). But except for the clouds, Earth doesn't shine bright white in images of Earth taken from cis-lunar space.

Here's an image of Earth seen from the Moon. Although it has 3 times as high albedo, it does not seem to be as bright as the white Moon is as seen on Earth's blue sky.


texts: What is the current accepted theory as to why Mercury, despite its size, has a similar density to Earth?

texts:
According to the NASA web page overview about Mercury, despite the planet being just a bit larger than our moon, it's density is about 98.4% of Earth's.  This high density suggests a comparatively large iron core (compared to the rest of the planet).

Recent studies reported in "NASA Antenna Cuts Mercury to Core, Solves 30 Year Mystery" (NASA, 2007) have confirmed the presence of a molten core, surrounded by a silicate mantle (depicted in the illustration below (from the article):

The question is then, what is the current accepted theory as to Mercury has a still-molten core and a density like that of Earth?


texts: Does the Milky Way belong to a Galaxy cluster

texts:
I know that the Milky Way is a member of the Local Group and the Virgo Supercluster / Laniakea Supercluster. However, I can't seem to find any information about the Galaxy cluster we belong to.

Does the Local Group / Milky Way belong to a galaxy cluster?


texts: Spotting the International Space Station (ISS)

texts:
Recently, I visited the NASA website which provides sighting locations to see the International Space Station (ISS). As we all know, we can even see ISS with the naked eye in a clear sky as a passing star without any blinking.

But unfortunately, I don't know how to measure the angle on the sky to see it. On the official NASA website there's given height (altitude) and direction as 21° and 11 above N respectively.

Here is the link: NASA - Spot The Station

How do I trace ISS?


texts: I want to know whether the temperature in Outer space is higher than earth's or cold.Is the temperature in outer space vary as it does on earth?


texts:
I assume they should be in the Milky Way galaxy. I have read about it a little but did not find information on where they are.

Which galaxy do the Pleiades belong to?


texts: Have any meteoroids been detected before they reached the Earth's atmosphere?

texts: Once a meteoroid starts burning up in the atmosphere, it becomes a visible meteor. Have any meteoroids been detected before they started to burn in the atmosphere? If yes, what is the ballpark estimate for the number of meteoroids detected before they reach Earth's atmosphere?


texts: What might a CN filter be in the context of comet watching? Is it showing dust, or gas, or something else?

texts:
In this post on the website for the Comet Wirtanen Observing Campaign at wirtanen.astro.umd.edu, there's mention of a CN filter being used to observe the comet, and this cool GIF.

What exactly is a CN filter? What wavelengths does it pass? Where can I read more about it? Why is it showing a spiral shape of stuff being emitted from comet 46P? Is this comet dust, gas, something else?

GIF:


texts: On (minuscule) dark matter production in supernovae

texts:
It is believed that dark matter is made of particles, which interact with matter only weakly and gravitationally. One common candidate for dark matter are so called WIMPs. WIMPs, specifically, are heavy and may be their own antiparticles.

And as any other particles dark matter particles can be produced at sufficiently high energies. The mass of dark matter particles is unknown, but is estimated to be of order $1$-$100 \textrm{GeV}$, which corresponds to temperatures of $T_{DM}\approx 10^{13}$-$10^{15}\textrm{K}$, at which these particles may be expected to be produced.

Such enormous temperatures are barely attainable in any reasonable astrophysical processes, but say in core-collapse supernovae newly formed core has temperatures of $T_{SN,after}\approx 10^{11}\textrm{K}$, and probably more during the collapse phase. Then a crude estimate would suggest that the amount of dark matter produced is $M_{DM}\approx e^{-T_{DM}/T_{SN,max}}M_\odot$. Or, in number form $\log_{10}(M_{DM}/\textrm{kg})=30.3-0.43(T_{DM}/T_{SN})$. This means that at $T_{SN}=1.4\cdot 10^{-2}T_{DM}$ the amount of dark matter produced during a supernova will be around one kilogram. Such temperatures are fairly reachable for $1 \textrm{GeV}$ DM particles. So one can optimistically expect few kilograms of dark matter produced per supernova.

Now the question. What is a typical dark matter production in core-collapse supernovae? A good answer, I imagine, would be a more robust expansion on the existing estimate. Any constructive comments are welcome.


texts: A question about the distribution of mass among the planets in the Solar System

texts: Is it coïncidence that the mass of a planet has about its maximum in the middle planets (Jupiter), while the mass of the closest and furthest planets has a minimum (Mercury and Pluto)?


texts: Could an impact have resurfaced Venus 300 million years ago?

texts:
Venus surface isn't older than about 300 million years. The only explanation I've come across is that some kind of global volcanism resurfaced the planet. But couldn't it have been an impact event? A huge comet hitting it by chance, maybe making Venus tip over and stop spinning too.

Or could Venus have had a moon like Phobos which spiraled inwards, disintegrated and rained down during a few million years? Phobos will do so in only 50 million years, maybe it is a common feature for terrestrial planets to form with such moons that hit them billions of years later. Maybe Earth is an exception because of the large Moon and how it formed.

Would an impact event leave visible traces like impact basins, or could the entire surface melt and reform as it is today, as I suppose Earth did when the Moon formed? Could Venus have been a very different planet up until 0.3 billion years ago? How could one find out, what kind of investigation would be needed?

Pluto's mass is about 1/50th of Mars (and Theia), so I suppose that it would be enough for a Pluto sized comet to have had about 7 times the impact speed compared to the pre-Earth/Theia collision. Comets could have up to 70+35 km/s speed relative to Venus. Someone maybe can make a rough estimate of what's needed to resurface Venus and how likely such an impact event would be?

And could reformation and redifferentiation after an impact have eliminated a previous magnetic field?

The diversity of the planets and moons, I suggest, depend more on their vast history of random events, than on where and how they once formed. I suspect that planetary scientists generally want to discount a unique planet reforming event only 0.3 billion years ago, just to make their job a bit easier ;-)


texts: How many galaxies are there in the Hercules–Corona Borealis Great Wall?

texts: The Hercules–Corona Borealis Great Wall is "to date (February 16, 2015), it is the largest and the most massive structure known in the observable universe" (source). How many galaxies is the Hercules–Corona Borealis Great Wall believed to contain?


texts: How should exoplanet discoveries affect SETI?

texts: Given that SETI was created before the discovery of exoplanets, has this changed how they search? Would it make more sense to focus efforts on discovered earth like exoplanets?


texts: What are the implications if the Sun was formed in a warm nebula?

texts:
Molecular oxygen O2 has been found on comet 67P/C-G in a ratio of 3.8% to water, which is much higher than expected. An explanation proposed is that the Solar System formed from a molecular cloud warmer at 45 K, than typical molecular clouds at 10 K. I speculate this could have had many kinds of consequences for the Solar System and wonder what the most important or easiest to detect would be.

For example, my uneducated guess would be that more hydrogen escapes from warmer clouds. Exoplanets with low density could then be the result of higher hydrogen abundance, more frequently than here giving them large hydrogen atmospheres.

News article

Ten minutes radio interview

(Haven't found any paper)

A star forming molecular cloud, for decoration.


texts: Is there a cosmic, rather than technological, upper limit to what a telescope can resolve?

texts:
Space radio interferometers could have a baseline of millions of kilometers, but is there a point where a larger baseline doesn't improve the resolution anymore because the photons observed are distorted before they arrive? This question deals with technological limits of resolution. I'm instead asking about cosmic limitations due to for example interstellar and extragalactic gas which scatters light.

This paper about results from the RadioAstron space/Earth interferometer is well above my pay grade, but it seems to be about this problem. The executive summary says:

  At longer baselines of up to 235,000 km, where no interferometric
  detection of the scattering disk would be expected, significant
  visibilities were observed with amplitudes scattered around a constant
  value. These detections result in a discovery of a substructure in the
  completely resolved scatter-broadened image of the pointlike source,
  PSR B0329+54. They fully attribute to properties of the interstellar
  medium.


texts: Distance to Proxima Centauri (Gaia VS New Horizons parallax program)

texts:
The current best parallax measurement for the nearest star to the Solar System, Proxima Centauri, has been given by the European Space Agency's Gaia mission. This is $768.5004\; \pm \; 0.2030 \; mas$ (milliarcseconds) as for Gaia Data Release 2. This puts Proxima Centauri at a distance of $4.2441 \;\pm\; 0.0011\; ly$. Therefore the uncertainty is so small that the error spans $141.8 \; AUs$, which is more or less the size of the orbit of the Dwarf Planet Eris. The precission is staggering, but if we want to send one day a light-sail mission to this system and explore its planets we will need two orders of magnitude greater precission in the distance estimates (to at least start talking on how to aim at the $AU$ level).

NASA's New Horizons team has launched an interesting proposal to measure the parallax of Proxima Centauri and Wolf 359 by using the Long Range Reconnaissance Imager (LORRI) onboard of the New Horizons probe. Gaia was made to perform these astrometric measurements with high accuracy (less than a milliarcsecond) and New Horizons was not. But while Gaia has a $\sim 2 \; AU$ baseline for the parallax measurements, New Horizons is at $\sim 47 \; AU$ from Earth (as for the 6th February, 2020). The team wants to get this new measurement for Proxima's parallax on April 22, 2020, using simultaneus observations from Earth and the Kuiper Belt.

I guess that the real baseline for the measurement can't be the entire $47\; AU$ between the spacecraft and Earth but something less (since the probe is not moving in the plane perpendicular to the Proxima - Earth line), but still it will be a huge increase with respect to Gaia's baseline. Still LORRI is not as prepared as Gaia to measure small angles.

So, my question is, How these two things (larger baseline but lower ability to measure small angles for New Horizons) balance out? Will the distance to Proxima Centauri get more accurate with New Horizons parallax program, or is Gaia going to still hold the record for that measurement with its $2\; AU$ baseline? And if New Horizons gets a more accurate parallax measurement, how large we should expect the error in the distance to be compared to the current $141.8 \; AUs$ uncertainty measured by Gaia?


texts: Will the United States Presidential Election (day asteroid) be back soon?

texts:
My google news feed is awash with mono-themed articles, including a near Earth asteroid that passed by around election day 2020 in the US.
We can all hope that neither will lead to an extinction level event :-)
My question is about the asteroid itself.

Will 2018 VP1 pass close to the Earth again this century?
Did it before?
Does this current pass have any particularly notable or consequential "keyhole-like" impact on its future orbit?

Cool GIF of several years of trajectory, about 5 MB so too large to embed directly: https://en.wikipedia.org/wiki/File:Animation_of_2018_VP1%27s_orbit_around_Sun.gif

Background on Keyholes:

Do all dangerous asteroids first pass through keyholes?
Understanding gravitational keyhole analysis for Near-Earth Objects
Gravitational keyhole for spacecraft flyby?


texts: What are the minimum element requirements for a star?

texts:
What elements would be essential for a star to exist?

From what I understand our sun is made of mostly hydrogen and helium and most stars have small amounts of heavier elements like carbon, nitrogen, oxygen and iron.

But could a sun exist on a single element such as Hydrogen? Or on another gas for example oxygen or nitrogen? Or even rare gases such as Neon or Xenon?

Is it even possible for a star to exist without any hydrogen or helium?


texts: Why didn't the Big Bang produce heavier elements?

texts:
Shortly after the Big Bang, temperatures cooled from the Planck temperature. Once temperatures lowered to 116 gigakelvins, nucleosynthesis took place and helium, lithium and trace amounts of other elements were created.

However, if the temperatures were so high shortly after the Big Bang, why weren't much heavier elements produced? 116 gigakelvins is obviously far above the temperature required for elements like carbon and oxygen to fuse. In addition, shouldn't most of the protons at those temperatures have fused, leaving the Universe with mostly heavier elements?


texts: Could the trajectories of non-periodic comets be used to infer properties of the 'ninth planet'?

texts:
Non-periodic comets are comets which have very long orbital periods (>200 years or more), spending most of their time in the outer solar system.

Planet X, recently revived by researchers at Caltech, is a proposed planet orbiting in the farthest reaches of the outer solar system. The Caltech researchers infer its presence from to its effect on the orbits of Kuiper belt objects.

If such a planet exists, and is the cause of the Kuiper belt object alignments, could it not also knock such objects in to the inner solar system, creating non-periodic comets with huge aphelion orbital distances? Could our current observations of non-periodic comets be used to infer properties of the planet?


texts: Can't see any detail on planets with my new Celestron NexStar 130 SLT Computerized Telescope

texts:
Mars looks like a small white blob/circle and the same with all other planets. This is very frustrating. I've looked all over for a solution jumping from site to site and nothing. Please be different on this site.

Edit: Many people have marked this post as duplicate. Yes, I know, but the other post did not answer my question.


texts: How does using Tidal energy affect the moon?

texts:
Reading another question Where do we have it from that the Moon is migrating away from Earth?
I makes me ask what effect does harvesting tidal energy for electricity production have on the rate the moon gains angular momentum?
Presuming the most common harvesting methods involve underwater turbines in tidal zones with water flowing regularly in both directions (twice per day).


texts:
In the book "Horizons: exploring the universe-Cengage learning (2018)", p200, it states that:

Helium fusion produces carbon, and some of the carbon nuclei absorb helium nuclei to form oxygen. A few of the oxygen nuclei can absorb helium nuclei and form neon and then magnesium. Some of these reactions release neutrons, which, having no charge, are more easily absorbed by nuclei to gradually build even heavier nuclei. These reactions are not important as energy producers, but they are slow-cooker processes that form small traces of heavier elements right up to bismuth with atomic weight 209, nearly four times heavier than iron. Many of the atoms in your body were produced this way.

Base on my question previously, I assume we are talking about the alpha process here. And when I check the Wikipedia of the Alpha Process, it says that the alpha process ends at $^{56}_{28}\mathrm{Ni}$ due to photodisintegration, but as the suggests, the process should produce $^{209}_{83}\mathrm{Bi}$. The question is, why do Bismuth, an atom with atomic number $83$ are produced here? Shouldn't atom like $^{}_{82}\mathrm{Pb}$ with even atomic number being produced here?


texts: Why can't we see Saturn's phases from earth?

texts:
In the Astronomy Picture of the Day from August 8, 2020 ("Crescent Saturn"), the caption states

From Earth, Saturn never shows a crescent phase

Why is this? We can observe phases on planets such as Venus which have an apparent size a lot smaller than Saturn. Saturn is not tidally locked to the sun (only Mercury is).
So why does the sunlit face of Saturn always face Earth?


texts: How much iron does a star fuse before going supernova?

texts:
I understand stars fuse atoms into heavier and heavier elements. When the star starts to fuse iron, the amount of energy released is less than the amount of energy it to takes to fuse the atoms. This creates an energy deficiency and the core is unable to maintain its outward pressure against gravity's inward collapse. The star collapses, rebounds against electron degeneracy pressure (I believe?) and goes BOOM. But how much iron is actually fused? And, for how long is the star fusing iron before the collapse?

Also, as a little bonus, I read somewhere recently that the presence of nickel is possible prior to going supernova. I can't find where though. Was that person wrong?


texts: Can you see the starting and the ending of a light beam passing in the distance?

texts:
This question arose to me when I saw a SciFi movie where they shot with laser guns and you clearly could see the dashes of light beams travelling from the shooter to the target. Nonsense of course, reality is much more boring.

But I wondered if you would just need more distance:

Given a limited light beam traveling from A to B, where "limited" means that there is a start and / or end of the emission source causing that beam.
Given enough distance from us to A, B and the line between them
And add some kind of nebular smoke in between just enough to disperse as much light as needed so we can see it here but not as much to prevent it from reaching B.

Couldn't we observe the starting and / or the ending of that light beam, progressing on it's way from A to B, like a jet trail in the sky?

If it is possible, where can this be observed? Or do the laws of physics forbid such a thing?


texts: Why do the asteroids orbit the Sun in roughly the same plane as the planets?

texts:
The asteroid belt between Mars and Jupiter is an extremely active environment (on an astronomical time scale) where collisions between 10km radius bodies occur every $10^7$ years, according to wikipedia.  It was likely much more active in the past, before many of the asteroids were ejected due to planetary resonances.
But even after all the collisions throughout the asteroid belt formation until now, the vast majority of currently existing asteroids have low inclinations with respect to the ecliptic.  That is, the inclinations of their orbits are roughly aligned with the rest of the planets' orbits around the Sun (credit figure to wikipedia):

Question: Why haven't all the collisions caused the inclinations of the asteroid belt to be more widely distributed?


texts: Does a rotating moon experience greater tidal heating than a tidally locked equivalent?

texts:
Tidal heating of a tidally locked moon is relatively straight forward to calculate, even though details of its internal structure is hard to work out in the first place.
By contrast, tidal heating due to tides of a rotating body is much more involved.

These two processes aren't completely equivalent. For instance, for a tidally locked body, the heating depends on the eccentricity, with no heating at zero eccentricity. By contrast, a rotating body can very much experience tidal heating even when in a completely circular orbit.
As a naive assumption, a rotating body will still receive heating from the deformation caused by an eccentric orbit, with some additional heat added through the periodic deformation caused by the rotation. As such, a rotating body will always receive more heat than a non-rotating one.
Which has the obvious use case that one can obtain a lower bound for the tidal heating through a simple calculation.
But is this assumption anywhere close to the truth?

Or, to put it in another way, two scenarios of moons in identical orbits. One tidally locked and the other not, which experience more tidal heating?


texts: Who coined the phrase "martian dichotomy"?

texts:
This question is adjacent to this other one.
The martian dichotomy refers to the fact that the northern and southern hemisphere are radically different on Mars, with different surface ages and different crustal thickness.
When was the phrase "martian dichotomy" used for the first time? By who?


texts: What color distribution does a protoplanetary disk have?

texts:
A kids question indeed, but I do not have a conclusive answer. An usual artist's impression uses red and yellow as dominating colors, and a rather homogenous, dense disk, but how reasonable is that?
If you follow e.g. Sciencedirect's teaser page on Protoplanetary disks

Dust grains are a relatively minor constituent of protoplanetary disks, but they represent the starting point for the formation of rocky planets like Earth, and possibly also gas-rich planets like Jupiter. These grains are small, typically 1 m in diameter or less.

Later on the same page:

However, the fact that roughly half of young stars have debris disks of dust thought to come from asteroids and comets implies that growth of large solid bodies occurs in many protoplanetary disks, even if the mechanism remains obscure.

This two statements for me seeded some doubts that homogenous red is really the correct color to associate with the inside of a protoplanetary disk.
I also found a paper by Alan P. Boss stating

Theoretical models of disks undergoing the accretion of mass from an infalling cloud envelope predict disk temperatures in good agreement with these constraints: a moderately warm (500–1500 K) inner disk, surrounded by a cool (50–150 K) outer disk.

This would at least support the color scheme if you assume black body radiation.
Related

What makes protoplanetary disks start rotating? (Initial energy needed to rotate)


texts:
Kepler data suggests that the vast majority of planets are smaller than 4 Earth radii, with larger planets quickly becoming vanishingly scarce. Yet somehow, our own solar system harbours not just one, but two giant planets. This seems suspicious.

Are giant planets expected to be as rare as the Kepler data suggests? Or is there some bias inherent in the transit method that makes detecting giant planets more difficult? Is it perhaps the long orbital period of a planet that formed outside the frost line that has caused this apparent dearth of giant planets?


texts:
I have downloaded the calibrated ffi(full field image) for the Kepler field, aside from the primary HDU which contains the metadata, they contain 84 channels, each in the form of an image HDU, representing a small part of the field - I want to plot the full field in astropy, how would I go about it?
The Kepler ffi file can be found in the link below
https://archive.stsci.edu/missions/kepler/ffi/kplr2013098115308_ffi-cal.fits


texts: How to accurately measure the temperature of red supergiants?

texts:
I just (February 28th, 2021) heard the news on progress how to measure the temperature of super giants:

Red supergiants are a class of star that end their lives in supernova explosions.
Their lifecycles are not fully understood, partly due to difficulties in measuring their temperatures. For the first time, astronomers develop an accurate method to determine the surface temperatures of red supergiants.

The original article by Daisuke Taniguchi and team is called Effective temperatures of red supergiants estimated from line-depth ratios of iron lines in the YJ bands, 0.97-1.32 μm but is not available (yet).
Maybe somebody can help me understanding the following quote intuitively:

However, by looking at the ratio of two different but related lines - those of iron - we found the ratio itself related to temperature. And it did so in a consistent and predictable way.

How could the ratio between the intensity of spectral lines correlate with temperature? Furthermore: How could we actually show that correlation if we do not know the temperature in first place?
References

What are the possible solutions to the Red Supergiant problem?


texts:
I have to find the perihelion and aphelion data for the 20th century for Earth. I found this table http://www.astropixels.com/ephemeris/perap2001.html, but no such table for the past century.

I think it can be found using JPL Horizons web interface, but can not use the code (the boundaries of the task I was given) and do not want to check 36000+ entries by eye to find maximums and minimums: this is not the general way to solve the problem.

I believe that there is some relationship between  Keplerian elements and perihelion (argument of periapsis or mean anomally) but after checking the file from JPL Horizons I could not find any such relationship. Therefore, I have two questions:

1) Is there an archive with the dates of peryhelion and aphelion in the past?

2) What is the relationship between Keplerian elements and the perihelion (of course, if such exists)? Unfortunately, I was not able to find it from the picture on https://en.wikipedia.org/wiki/Orbital_elements. More precisely, is it true that argument of periapsis or mean anomally is equal to 0 at the perihelion?


texts: Planning observation: determine dates where moon is within 30 degrees of my object?

texts:
I'm planning an observation for a proposal and I need to determine which dates the moon is within 30 degrees of an object so I can ask to not be scheduled for those dates.  This object is near the ecliptic so it is guaranteed the moon will pass close by at times.

In the past I've used skycalc to manually figure out such dates, but now I need to figure out dates over a several month period, and I was hoping there was some more automated tool I could use for this purpose.


texts: How does the Milky Way look like above 66° North and below 66° South?

texts:
I read on Wikipedia:

  depending on the time of night and the year, the arc of Milky Way can
  appear relatively low or relatively high in the sky. For observers
  from about 65 degrees north to 65 degrees south on the Earth's surface
  the Milky Way passes directly overhead twice a day

What happens and how does the Milky Way look like out of that range?
If it matters, consider also the all-summer light and the dark winter.


texts: Replenishing hydrogen in the core of the sun

texts: How is hydrogen supplied to the core of the sun? Shouldn't the radiative zone prevent this? Shouldn't heavier helium fill the core? How much of the hydrogen can the sun fuse?


texts: How much of the Milky Way is visible to the naked eye from earth?

texts: When we see the Milky Way on a dark night are we seeing the bulk of the galaxy, or just our local arm? How much of the milky way is visible to the naked eye on a dark night?


texts: How to convert between spectra given in terms of velocity (km/s) to wavelength spectra?

texts: I have H alpha spectra of H II regions in our galaxy. In the paper, the x-axis is in units of km/s and the corresponding line width as well. From this, how can I get equivalent width of the H alpha line?


texts: List of galaxies with their dark matter halo

texts:
Where can one find the list of galaxies with their dark halo masses, I've searched several sites but I found no such proper list where the masses of their dark matter halo is compiled?
Can anybody help?


texts: What is the origin of the OBAFGKM classification system?

texts:
Once a body has been identified as a star it is classified into a subsection of either O,B,A,F,G,K or M (I think there are also 3 more letters recently added)

What is the origin of this classification system? Do each of the letters stand for anything?


texts: Black Hole / Hawking Radiation: Why only capture anti-particle?

texts:
I may have some specifics wrong here.  If so, don't focus on those.  Just focus on the general thrust of my question.

I "understand" (cough) that particle/anti-particle pairs form spontaneously in space.  I understand that they can form near the event horizon of a black hole, and that one particle can fall in, where as the other particle can barely escape.  I understand that an anti-particle will annihilate with a particle.  What I don't understand is why only the anti-particles of these virtual particle pairs fall into the black hole, while the other ones just manage to escape.  Shouldn't both particle and anti-particle have equal chance to be the one to fall in, or just manage to escape?

It seems that there should be an equal chance of either the particle, or the anti-particle, would be captured while the other "ejected."  So it seems that the black hole should be somewhat steady-state as far as mass change with respect to virtual particles.

Explain?


texts: Why can I see the dark side of the moon?

texts:
Last weekend (29/30 April) the sky in my area (Central Europe) was pretty clear and the Moon was nicely visible. Funnily, one could not only see the sunlit area of the Moon, but also the dark side* could be easily recognised throughout the whole evening from blue hour until dark night. I attached two photos of the Moon that should illustrate the effect. The pictures (sorry for the poor quality) needed to get a little overexposed to capture the illuminated dark side, but with plain eye the effect could be well seen.
We were speculating about the reasons why the non-sunlit area of the Moon could be seen.

diffraction of sunlight through the atmosphere can be neglected as the Moon doesn't have an atmosphere.
reflection of light that in turn was reflected from earth (Sun -> Earth -> Moon -> observer) sounded a little unlikely to me
a psychological effect that kind of mentally completes the shape of the Moon, because we know it should be circular, sounded ok to me. But could be debunked as the dark side stays visible if one covers the bright side on the photo?

So I guess the  sunlight has to reach the dark side of the Moon somehow differently.

What could be provide enough light to make the dark side visible?

* not the far side of the Moon, but the non-sunlit area of the Moon


texts: Would it be possible to discover an asteroid belt around another star?

texts: With existing or planned technology (e.g. the ELT or the JWST), would it be possible to infer the presence of a ring of asteroids similar to our own asteroid belt? Or would any signal be drowned out in the noise?


texts:
I read about the LIGo experiment recently, but i didn't understand their significance. Although, it's clear to me that the gravitational waves do exist and are caused by large accelerating bodies in space.

but how are they significant to Humans as we do not have any mechanisms for harnessing these waves and Don't know what use they may be of.


texts: If a comet strikes a glacier, does it make a print on the land below?

texts:
The Younger Dryas Impact Theory describes an asteroid impact in Northern America, possibly the eastern part of Hudson Bay, which contributed to the end of the last ice age.

If a comet strikes a glacier, would it make a print on the land below? If specifically the comet that made this impact crater in Hudson Bay, and a glacier that was maybe comparable to Antarctica so 2 km thick.


texts:
What exactly does p-wave mean when referring to particles, like charmonia states.

For example, see the following reference:

http://arxiv.org/abs/hep-ph/9208254

My doubt is - p wave in scattering means l=1. But how is that used to label a particle state?

Thanks.


texts: Why isn't the relativistic jet visible in the image of the M87 black hole?

texts:
I'm referring to the infamous relativistic jet, which consists of matter being accelerated to near the speed of light, originating at the poles of the black hole:

But in the image of the black hole in the radio spectrum nothing of the sort is visible:

I would expect the relativistic jet to be one of the most prominent features since it's accelerated much more that other material orbiting the black hole.

Is it because the jet is more prominently visible in the visible and infrared spectrum than in the radio spectrum?


texts: whose gravitational pull is more stronger , Neutron Star or Black hole?

texts: We know neutron star is very densest in the universe and it weighs the thousand times of our Sun. And Black hole having strong gravitational pull not even light can escape From it . So , whose gravitational pull is greater ?


texts: I was wondering if there is an established method to keep track of the orbit of an exoplanet assuming we know a - the semi-major axis of the orbit, e - the eccentricity of the orbit, and i - the inclination of the orbit. Can we track its position once a month?


texts: Is it possible to model a solar thermal concentrator using Zernike polynomials?

texts:
This question might seem a bit off-topic, but I guess there are a lot of people here that know about optics, telescopes, etc.

I would like to simulate solar thermal systems that focus solar radiation, e.g. heliostats or dish Stirling. Usually they are simulated using raytracing or Gaussian cone optics.

Basically, I would like to simulate the optical system and get the resulting image of the sun on some surface.

In the end I would like to calculate the "flux distribution" (~brightness) of the reflected radiation on some sort of receiver. The receiver could be a plate with heat pipes beneath or a Stirling motor. I would like to create images like http://solarenergyengineering.asmedigitalcollection.asme.org/data/journals/jseedo/929668/sol_136_03_031013_f002.png

So far, I read that Zernike polynomials can only be used to simulate optical systems with circular apertures. This is not the case for my application. Currently I am evaluating the optical system using Monte Carlo raytracing (GPU based) , which yields the very high accuracy that is needed.

We have not done any work on this so far, but for very large mirror arrays, e.g. 25000 heliostats, the raytracer takes quite a while to converge. And calculation time is a very critical point when in comes to optimizing the positions of the mirrors to avoid the shading and blocking amongst them.

This is why we are looking for faster ways to evaluate the optical performance of these systems while still getting highly accurate results.

Do you think it is possible to simulate them using Zernike polynomials? The simulation needs to consider surface errors of the mirrors, astigmatism and non-ideal focal lengths.
Can one use Zernike polynomials only for arbitraty optical systems?


texts: is there a way to determine a distant galaxy’s speed relative to the Hubble Flow by measuring time dilation effects between there and this galaxy?

texts: As I understand it there is a preferred frame of reference based on the velocity for the CMB and our galaxy is moving in relation to it (at about 600 km/s). I think this is how the Hubble Flow is defined. Given that there are no relativistic effects, and I really mean time dilation, between distant galaxies that are moving apart due only to Cosmological expansion, is there a way to determine a distant galaxy’s speed relative to the Hubble Flow by measuring time dilation effects between there and here? If so using that and observed red-shifting, one could establish a more accurate measurement of the Hubble Constant.


texts: Any plans for TESS after it finishes northern sky survey?

texts:
TESS has provided the astronomy community with a treasure trove of information.

Once TESS completes its one year survey of the northern sky, are there any plans for an extended mission?
Just seems like 27 days is too short to look for three transits of planets orbiting in the habitable zone of M dwarfs.
Approximately what percentage of planets orbiting M dwarfs in the habitable zone and transiting our line of sight would be missed by 27 day observations?
Are there plans for follow-up observations with telescopes on Earth of 1 or 2 transit events picked up by TESS to confirm planet or not?

Looks like it was a very successful mission with data that will be useful for many years to come.


texts: Why didn't the Event Horizon Telescope team mention Sagittarius A*?

texts:
At the press conference this morning, the Event Horizon Telescope team didn't say much about Sagittarius A*, which was the target many of us have been waiting for.

Is there any explanation anywhere for this omission?


texts:
Imagine two cubes each with the side 1 light year. One of the cubes is empty of any matter. The other cube contains a massive star.

Does the cube which contains the massive star have a larger volume than the empty cube? (Because the mass makes space curvy)
If the star is replaced by a gas cloud of the same mass but which is evenly distributed inside the cube, does the volume of the cube change?
Is it not enough with geometry to calculate volumes? Is knowledge of the mass (and its distribution?) also necessary?
Does mass (concentrations) create new space volume, or does it just change the properties of the space around it?


texts: Seeing a line rather than a dot when looking through refracting telescope

texts:
I bought an amateur(and rather cheap) refracting telescope and while I can see moon quite clear and crispy I am having difficulties in observing some larger stars.

All stars appear as lines rather than dots. It is always one longer line. I read something about those lines but this stands only for reflecting telescopes that have some kind of structure inside that holds a mirror and this structure interfers thus producing these lines. But I don't have a reflecting telescope, mine is refracting.

I cannot seem to find anything on google regarding this. Maybe it is because I lack the vocabulary.

EDIT #1:

This is the telescope I have.

Edit #2:

This is my depiction of what I see. Forgive my MS pain skills. As I focus out(or in, not quite familliar with the naming) it goes more clearer and clearer but I never get to see a simple shiny dot. The closes to dot is the first image but this is so blurry that I barely see it. The red line is the one I perceive as the clearest. The orange lines is what I perceive as "outline" and the yellow inside is that shiny effect one usually gets when looking at objects that emmit light.


texts: I've heard the universe is just an empty cavity. Does the universe have any edge or stop or is it just an infinite empty cavity?


texts: Why is the peak value(s) of the spectral radiance of the CMB different if you calculate with freq. instead of wavelength?

texts:
On Wikipedia, the calculated value of the peak frequency of the cosmic microwave background is 160.23 GHz, but it says if you do the calculating with wavelengths, then convert to frequency, you get a value of 282 GHz.
Why the difference?
There used to be an answer on Quora, I believe, but I can't find it anymore...
Something to do with the summation using integral calculus, I believe...


texts:
What frequency distribution law applies to a random point in deep space that is assumed to be far away from any particular source of radiation.

Can it be expressed by some form of Plancks/Bose-Einsteins/Fermi-Diracs laws or a mix of all of them?

What would be the mean frequency/wawelength?

Would the mysterious "dark energy" be a major contributor to the distribution?


texts: Why are blackholes generally not considered as solid spheres with an escape velocity FTL?

texts:
I was reading Do Stars Vanish Into a Black Hole or Crash Against a Surface? A New Test Answers on space.com.
It says the following:

Another proposed alternative to event horizons is the "hard surface
theory," which suggests that matter within a black hole is destroyed
by smashing into a solid surface. Instead of a singularity with no
surface area, the black hole is a giant mass with a hard surface, and
material being pulled closer — such as a star — would not actually
fall into a black hole, but hit this hard surface and be destroyed. If
that were the case, the collision should create a large burst of
light.

If we focus on the last sentence:

If that were the case, the collision should create a large burst of
light.

If the escape velocity of black hole becomes at certain altitude above the say solid surface of a blackhole more than that of speed of light, would we still see a large burst of light when the collision happens? Black holes are incredibly dense wouldn't it make more sense from them to be solid?
Something like a dark star.
No one really knows what happens to the matter at the singularity. Wouldn't it make sense that the reason that a black hole gets larger is due to more matter being smashed into the singularity making it gain mass. It also seems that black holes can be hurled out their galaxies, it must be in some form of matter that it stays together even when hurled out?


texts: Could gravitational waves near merging black holes collapse to a black hole themselves?

texts:
I have understood that merging black holes emit considerable amount of their mass as gravitational waves (up to 5-10%). Based on what I have understood from gravitational waves, the closer black holes are to merging, intensity (both frequency and amplitude) of these waves become stronger.

I am thus assuming much of the total GW output happens during the last "orbit" of the inspiral, and that the origin of these waves is located within "the final orbit", i.e. really close to event horizons of both black holes, my question is essentially, is it possible for such GW to collapse into a black hole themselves (something like a kugelblitz I believe), since there's just a lot of energy in GWs (say a few solar masses) in such small volume of space (say tens of kms cubed)?

I believe this might depend on the size of merging black holes, as both intensity of GWs as well as size of event horizons depend on the mass. I have a gut feeling that smaller black holes might be closer to this limit but maybe both the intensity and event horizon size depend linearly on the mass, and this does not matter at all.


texts: Is there any difference between parallel universes and multiverse?

texts: Nowadays we come across with these two terms - parallel universes and multiverse. I wonder if this is the same thing or its two entirely different principles because the names are a bit confusing to me. Can anybody please shed some light on this?


texts:
Where can I find the
dataset(s) for a globular star cluster?

The datasets should have the coordinates, color index (for different wavelengths) , magnitude etc. of every star in the cluster.

I want to do data analysis on it just for fun.


texts: Can you find your own location in space by measuring angles between stars?

texts:
Imagine you have 3 star points in 3D space A,B and C.
From your unknown position P in space you can measure the angles APC, APB, BPC and you know coordinates of A,B and C and therefore the distances between AB,BC,CA. Is there a way to calculate your own position P? Imagine you are floating in space and you're not on a sphere like earth.

Perhaps this is a frequent problem in astronomy and am wondering if there are any techniques to solve it. If you think there is, please point me in the right direction!

Greetings,
Matlab M.


texts: Are these real paths of planets as traced from Earth?

texts:
Few days a go, I came across these two pictures of paths of planets as observed from Earth. They have a perfect geometric shapes.  Actually, to me they look so beautiful and perfect, that they appear fake or made by a pseudo-scientist or some propaganda society (e.g. flat Earth like community people) who talks about divine geometry etc.

Auxiliary questions: Is this the reason, why Earth was consider to be in the center of the solar system?


texts: Computing radial-velocities from Cross Correlation data

texts:
How can I better fit a Gaussian curve to a CCF so that I get the most precise RV value? The image below shows the fitting where I compared the fitting by weighting by the uncertainties and not. There is not a big difference between them because the errors are nearly the same for all data points.

The RV is the $\mu$ and the uncertainty was gotten from the covariance matrix first time in the diagonal. Performing a similar procedure but for summing several orders (such as fig. below) gives me the RV time-series which has too much spread. I need to find a way to reduce the noise as much as possible. I am not showing the errors in RV time-series because I thought it to be coming from the covariance matrix but it looks unrealistic (too big).


texts: Can one calculate the size (i.e. the radius) of our universe?

texts:
If one can estimate the mass of our universe, might one also calculate its ultimate size, (after it fully expands), based on the Schwarzschild formula for the radius of a black hole? Please note that this simple formula
$$R=\frac{2GM}{c^2}$$
informs us that larger black holes are less dense. So, if it turns out that our universe is in fact a gigantic black hole, then one would expect it to be extremely low-density!


texts: How are galactic rotation curves determined from radial velocity measurements?

texts:
I have been reading about the deviation of galactic rotation curves from the predicted Keplerian curve to a flat curve at large galactocentric distances.

They were the first indicators of the existence of dark matter but I do not understand how the curve is obtained from Doppler shift data (as mentioned by some papers as the method of determination for the curve.)

Doppler shift data would allow measurement of radial velocity but how can that alone be enough to extrapolate the rotation curve?


texts:
Is it possible to send data using cosmic rays?

Like sending high and low energy cosmic rays, since they can travel farther. And this data can be converted to binary form that can be processed by computers.

I'm not an astronomer or studied any thing related to astronomy, I was just imagining if this is possible.


texts: Using a telescope to look at the Earth History in Some Detail

texts:
The following paragraph is a scientific fact.

When we look distantly into the universe (with telescopes) we see galaxies
(or whatever else you see) as they were millions years
ago- in other words it is how they looked in the past (this is because of the speed of light).

So my question is could we build a technology (using current science or more speculative/theoretical science) using this scientific fact too see the earth history or past to such a level of detail that we could see historical events (e.g. individual dinosaurs) and the famous people's faces (in history books) - as if we were standing face to face with them- of the long ago past? What's the best level of detail could we theoretically see?


texts: Would a future hole in the Cosmic Microwave Background show us the edge of the universe?

texts:
If my understanding is correct, the Cosmic Microwave Background always come from our event horizon. By event horizon I mean the edge of the observable universe.

If the universe is finite does it mean that after some time (maybe in billions of years?) there will start being a hole in CMB. As our event horizon let us see CMB from regions further and further away, isn't there a time where it will reach the edge of the universe?

If this is the case, based on the known number of atom and mass of the universe, is it possible to calculate when this will happen?


texts: Is it possible make artificial gravitational waves?

texts: Is it possible to generate gravitational waves (creating low or high disturbance in space-time) from very heavy bodies spinning at very high speed artificially?


texts: The Sun currently has a stellar class of G2V. However, since its birth, the Sun has brightened significantly. What would the Sun's class have been when it was born ~4.6 gyr ago?


texts: How are cardinal points on horizon defined?

texts: How are the cardinal points (North-East-South-West) defined? On equatorial regions it is somewhat obvious. But what about the higher latitudes? If the pole star is up above the sky instead of horizon, how do we define North? What is the case on the geographic poles?


texts: How to convert density from physical unit to comoving unit?

texts: I am learning co-moving units and I am interested to see how the conversion works. If Hubble constant is assumed to be 0.7, then I want to convert $1gm/cm^3$ into comoving unit. If I want to express length in co-moving kilo-parsec per hubble constant (${\rm ckpc}/{\rm h}$), instead of cm, then how does the conversion happen?


texts: Where does Love's number come from in $\delta m = \frac{1}{2}k_2M_2\lbrace\frac{R_1}{r_\star}\rbrace^3$, the formula for the mass of a tidal bulge?

texts: My question refers to page 165 of this paper. Specifically, how does one derive the equation $\delta m = \frac{1}{2}k_2M_2\lbrace\frac{R_1}{r_\star}\rbrace^3$ for the mass of a tidal bulge? A full derivation would be much appreciated, and also an explanation as to where Love's number $k_2$ comes from.


texts: How did Biden become VP? (naming of 2012 VP113)

texts:
The Carnegie Science article Solar System's Edge Redefined describes the discovery of the object 2012 VP113.
Wikipedia's article 2012 VP113 says:

Nickname:
2012 VP113 was abbreviated "VP" and nicknamed "Biden" by the discovery team, after Joe Biden, who at the time of discovery, was Vice President (VP) of the United States.11
11 Dwarf planet stretches Solar System's edge

and the referenced Nature News item says:

The newfound object's official name is 2012 VP113, but the discovery team calls it VP for short, or just 'Biden' — after US Vice-President Joe Biden. In several years time, after observations have pinned down its orbit, the scientists will submit a name for consideration by the International Astronomical Union (IAU), the organization in charge of celestial nomenclature.

Question: I understand that VP is short for Vice President, but where do those two letter codes come from? Is the VP in the object's name short for something literal (did the team choose these two letters?), or just a random computer-generated code, or something else?


texts: Difference in creation of solar flares and CME?

texts:
What is the difference in the creation process of solar flares and CME (coronal mass ejections)? How do they relate to sunspots and coronal holes?

Here there are some good explanations about the flares' and CME's differences. But my question focuses on how each of them is created, and what are the respective conditions at the corona.

Edit:
In an effort to make the questions more clear, I could add that as far as I can tell both effects result from magnetic reconnection, but in one case we have only energetic particles emitted while in the other we have whole chunks of plasma. Do we know which is the determining factor about which of the two will happen?

Also, I understand that flares are mostly related to sunspots while ejections are to coronal holes. Is this correct? If yes then it sounds like a pretty big difference.

(Please be reminded that specifying that the answer is not known yet is an answer.)

Edit #2: Please see this comment for further clarification of what the question is about.


texts:
If in our neighborhood of the Milky Way, the typical spacing between stars is 1 parsec, and the relative velocities between neighboring stars are of order 20 km/sec, what would the spacing between stars be in a scaled-down model in which stars are replaced by grains of sand (1 mm in diameter)? How fast would these sand grain sized stars be moving? [This is a quiz question from The Teaching Company's Introduction to Astrophysics by Joshua Winn.] The given answers are 44 km and 0.9 m/s.

I used the size of the Sun as a typical star (perhaps not accurate) and calculated the ratio of a sand grain's diameter to the Sun's diameter. I then multiplied this by 1 parsec (= 3.09 x 10^16 m) to get 21 km. This is about half the given answer so I thought maybe our Sun is not average sized.

I used the same calculated ratio and multiplied it by the give star velocity and got 1.43 x 10^-5 m/s. This is way off the given answer. What am I doing wrong? Is my calculation for the first part also wrong?


texts: Changing Appearance of the Moon During a Single Night

texts: I have noticed that the inclination of the moon at a given location varies throughout the night. From the UK, the terminator in a half-moon is clearly sloping from top left to bottom right early in the evening, but later on, as the moon is setting, it is clearly sloping from top right to bottom left. I know that the shape of the moon changes from night to night, but I just can't see why the inclination would change during a single night. I know that the appearance of the moon is due to a combination of the tilt of the earth's axis and the latitude of my position (the moon slopes oppositely in the southern hemisphere), but I just can't visualise in three dimensions exactly what is going on. Please can you help me to do this.


texts: How can the Advanced Composition Explorer (ACE) warn of incoming solar storms?

texts:
How can the Advanced Composition Explorer (ACE) warn of incoming solar storms when is is invested with radiation?

Discovery.com article Solar Storm Warning Satellite on Last Legs states that:

  Until the sun's free-flying and highly energetic outbursts, known as
  coronal mass ejections, hit the ACE spacecraft, forecasters don't know
  the orientation of their embedded magnetic fields.

I read that it can give 15 minutes in advance warning to Earth of the presence of an incoming solar storm. However to do that, it sends a radio signal which goes at the same speed of the solar storm so it will presumably take 15 minutes as well?


texts: What do these statements about interstellar magnetic fields really mean?

texts:
Quanta Magazine's The Hidden Magnetic Universe Begins to Come Into View is a fascinating review of a rapidly evolving field in astronomy.
It contains some statements that I feel are important to understand, but I don't.

However, once a “seed” magnetic field arises from charged particles in motion, it can become bigger and stronger by aligning weaker fields with it. Magnetism “is a little bit like a living organism,” said Torsten Enßlin, a theoretical astrophysicist at the Max Planck Institute for Astrophysics in Garching, Germany, “because magnetic fields tap into every free energy source they can hold onto and grow. They can spread and affect other areas with their presence, where they grow as well.”
Ruth Durrer, a theoretical cosmologist at the University of Geneva, explained that magnetism is the only force apart from gravity that can shape the large-scale structure of the cosmos, because only magnetism and gravity can “reach out to you” across vast distances. Electricity, by contrast, is local and short-lived, since the positive and negative charge in any region will neutralize overall. But you can’t cancel out magnetic fields; they tend to add up and survive.

Questions:

What does the phrase "...magnetic fields tap into every free energy source they can hold onto and grow..." refer to in the astronomical context of interstellar space?

What does the phrase "...only magnetism and gravity can “reach out to you” across vast distances. Electricity, by contrast, is local and short-lived, since the positive and negative charge in any region will neutralize overall. But you can’t cancel out magnetic fields; they tend to add up and survive." refer to in the context of interstellar space? Is it the lack of free magnetic monopoles, or the dearth of polarizable ferromagnetic material?


texts: Why do GPS satellites move in relation to earth's surface?

texts: Wouldn't it be easier with geostationary satellites? Has is to do with the monitoring of gamma-ray bursts?


texts:
The mass of Venus seems rather complicated to determine to me:

Venus doesn't have any satellites, so you can't just apply Kepler's third law (like you would with Jupiter or Saturn for instance) to determine its mass.
The gravitational tug of Venus on the Sun is very small compared to that of other Jupiter or Saturn, so it seems like it would be difficult to extract what part of the Sun's proper motion is caused by Venus.
There are few asteroids with orbits close to that of Venus, so not many objects who might have their trajectory modified by Venus.

Knowing Venus' radius, and assuming it has the same density as the Earth, you can get a pretty close estimate of its mass (85% of Earth's mass with this assumption, when the actual value is 82%). But that's a pretty strong assumption (the density of Earth and Venus only happen to be close by chance) and a rather unsatisfactory "guesstimate".
Nowdays, there are a few probes that have flown by Venus, so by looking at their trajectory, you can infer what Venus' gravitational field looks like. But those fly-bys are pretty recent. Did we know about Venus' mass before those fly-bys?
How was the mass of Venus measured for the first time?


texts: Why don't planets give off their own light?


texts:
Five billion years from now, the sun will have grown into a red giant star, more than a hundred times larger than its current size.
  While this metamorphosis into the giant star will change the solar system, scientists are unsure what will happen to the third rock from the sun.We already know that our sun will be bigger and brighter, so that it will probably destroy any form of life on our planet.
  But whether the Earth's rocky core will survive is uncertain.
  At the end of its evolution, seven billion years from now, the sun will become a tiny white dwarf star.

(by Leen Decin, professor at the KU Leuven Institute of Astronomy (source))

When our sun runs through its last phase of its life it will expand and tremendous solar flares will flow out of it. Earth will end up getting baked and will lose its atmosphere.

Jupiter is a gas giant planet, a GAS GIANT. So,

What will happen in Jupiter? Will it evolve into a star since it contains hydrogen and helium? How will the atmosphere deal with the extreme heat?


texts: Why do the planets in the Solar system stay in the same orbital plane?

texts: An earlier question addressed why all planets formed in the same orbital plane, but how is this angle maintained? What prevents the planets from taking on a different orbital plane?


texts: I read recently that a red dwarf star might actually look white.   I realize there's a wide range in red dwarf surface temperature, 2,500 to 3,500 degrees K, compared to 5,778 for our Sun.   Metal at 2,500 degrees K is nearly white hot with just traces of yellow.   Is that true for 93% hydrogen 7% helium as well?   Would the color of red dwarf stars be closer to yellow/white rather than red based on our vision, if we were to be close enough to get a good look?


texts: Do boulders erode differently on asteroids than on the Moon?

texts:
If I understand it correctly, boulders on the Moon are only found near fresh craters, because micrometeorites erode them over time. Asteroids are believed to have formed sometimes even earlier than the Moon, but some images show asteroids covered by boulders. And NASA is planning the ARM mission to go pick up a boulder from an asteroid.

Are boulders more frequent on asteroids than on the Moon, and if so, by what kind of mechanism? For example, it is not primarily micrometeorites, but temperature changes that erodes them on the Moon. Or don't microgravity objects attract as many micrometeorites as the Moon does?

Intact boulders on asteroid 25143 Itokawa:

Eroded boulders on the Moon:


texts: Infrared telescopes, magnitude and observations

texts:
Currently 22-23 magnitude could be the limit to make a spectrum for ground based 10m class telescopes, 21-22 magnitude may be easy for them.
4m class telescopes could possibly handle 20 magnitude, I am not sure.
2m could be appropriate for stars brighter than 16magnitude generally.

What about the infrared bands: J H K W1 W2 respectively? Are there any empirical values or references?


texts: The largest discrepancy in the history of science

texts: I watched a cosmology lecture given by Leonard Susskind that convinced me to put my money on dark energy being a pressure caused by energy that is evenly distributed throughout the "vacuum" of space. However, quantum physics predicts that there should be a much larger energy density (i.e. many magnitudes larger). Have there been any more recent findings or theories that could shed light on this discrepancy?


texts: What does a pulsar look like if viewed from above?

texts:
Have we ever seen a pulsar directly from above or below it's spin axis?

I am wondering if a pulsar seen from this angle would appear to be constantly spinning or if it would just appear like a normal star.


texts: Are there any known low-inclination trans-Neptunian objects?

texts:
All the trans-Neptunian object's orbits I know are very inclined compared to those of the eight recognized planets, and Centaur's orbits are highly inclined as well.
Are there any known Centaurs and/or trans-Neptunian objects or TNOs whose orbit isn't significantly inclined to the ecliptic or to the invariable plane, but is on about the same plane as the eight main planets?
And to double check, the hypothetical planet Nine also has a high orbital inclination, doesn't it?


texts: Error when calculating Alt/Az from Ra/Dec

texts:
I wrote a program based on this tutorial: http://www.stjarnhimlen.se/comp/ppcomp.html to calculate altitude and azimuth of a celestial object. When I compare the calculated RA/Dec values to the ones from Stellarium, they are very accurate. But when I compare the Alt/Az values to the ones from Stellarium, there is an error of about 2 degrees! I use the following method to calculate Alt, Az:

GMST0 = Ls + 180_degrees # Ls = Sun's longitude
GMST = GMST0 + UT
LST  = GMST + local_longitude
HA = LST - RA

x = cos(HA) * cos(Decl)
y = sin(HA) * cos(Decl)
z = sin(Decl)

xhor = x * sin(lat) - z * cos(lat)
yhor = y
zhor = x * cos(lat) + z * sin(lat)

az  = atan2( yhor, xhor ) + 180_degrees
alt = asin( zhor ) = atan2( zhor, sqrt(xhor*xhor+yhor*yhor) )

Some specific example:

Test date 15.09.2018, time 15:00 UT
Planet: Mercury

Coordinates: +47.55777777° +8.89888888

What stellarium says:

RA = 11h 18m 13.26s

Dec = +6°25'08.5"

Az = +250°21'13.2"

Alt = +25°25'00.1"

What my program says:

RA = 11h 18m 14s

Dec = 6° 25' 6.59"

Az = +248° 49' 6.9"

Alt = +26° 33' 16.43"

Thanks in advance!


texts: How did TESS scientists choose which stars to observe at a "2 minute cadence" in each field?

texts:
The BBC news podcast Science in Action episode New Planet Hunting Mission covers the upcoming TESS mission between 01:00 and 07:15 with Sara Seager, TESS deputy director of science, Massachusetts Institute of Technology, Cambridge, Massachusetts.

After about 05:00 Dr. Seager mentions that the TESS spacecraft will measure a special set of order 20,000 stars in each camera's 24x24 degree field at a two minute cadence.

How were the stars in each field selected for TESS?

The excellent YouTube video Transiting Exoplanet Survey Satellite (TESS) nicely explains how TESS operates and will slowly tile the celestial sphere.

below: From see TESS Operations. Click for full size.


texts: Does the quantity of dark matter needed in the Milky Way to give the stars their speed compare with the speed of the Milky Way?

texts: Dark matter was needed to give the stars in a spiral galaxy a cause of their speed. So they proposed there must be some extra dark matter in the Galaxy. The total extra mass of dark mater is quite high. As a consequence of that, the whole galaxy becomes much heavier. But in the group or a cluster, the Galaxy also has a speed relative to other galaxies. So my question is whether the mass needed to give the stars their speed is the same mass that is needed to explain its movement within its cluster or a group?


texts: Do origin theories imagine each planet to first orbit the Sun very irregularly before stabilizing?

texts:
What I was wondering is that, for example, toss a few balls into zero gravity space randomly, what would be the steady state motion?   Would not all the balls go on weird directions and undergo irregular orbits due to the interacting and irregular gravitations. I imagine the largest or more dense planets to begin to influence the smaller and eventually it would stabalize.  Is this what origin of the universe theories imagine, or am I totally missing something here? Would the smaller ones eventually all rotate around the largest? All in the same plane, more or less, and all in the same direction? It seems possible but I have no idea if this is mathematically derivable.

What are theories that explain chaotic motions into the present, same plane, same direction planetary orbits around the Sun?


texts: I know there are several theories as to how the universe might end, if it does. Is it possible for it to end by time stopping? A friend of mine told me about this theory, but her explanation that it would be caused by heat death doesn't have me convinced.


texts: Did atoms in human body indeed come from stars?

texts:
I think I am not alone who saw videos about that we (humans) are made of same atoms which someday were in stars. In other words, some atoms in our bodies are from stars which exploded billions of years ago.

I wonder if it is indeed true. I mean human's life begins when sperm cell fertilize egg cell. Now does that sperm cell or egg cell indeed contains some of the exact atoms from those stars?

I know little bit strange question, but would be interesting to hear if it is indeed true, that atoms in our body are same which someday were in stars.

In case you are wondering that's the video I am talking about: http://www.youtube.com/watch?v=9D05ej8u-gU


texts: What cosmic disaster is most likely to happen?

texts: Of all the different ways that the Earth can be destroyed what ways is the most likely that could happen?


texts: Does the sun's rising/setting angle change every few months?

texts:
When I lived in Darwin, Australia, I noticed that the Sun set in a slightly different direction to the West. In the evenings, I used to sit on a couch and watch TV. There was a huge window to my right and the setting sun would always shine bright into my face. So I moved a single vertical blind to block it out just about right. In the months of October/November I started noticing the sun shining into my eyes again. Neither the couch nor the blind had moved. After moving the blind again to block the sun, in a few months I would have to move the blind again. I was living alone and there is no way the blind or the couch would move.
When I lived in Canberra, Australia, I had the habit of stepping out of my house early in the morning. I would face the sun as soon as I stepped outside because it was too cold and I wanted the warmth of the sun on my eyes/face. I noticed again in October/November that my usual position of facing the sun was wrong. The sun would rise from a slightly different angle. So if earlier the sun was rising at 130 degrees from my door, it would now be rising at 110 degrees. The door faced the southeast, and because of the very narrow path and vegetation from my door I am very certain of my positioning.
I really don't know what this phenomenon is called. When I lived for so many years in other countries, I never noticed this. Am I just being silly or does the Sun rise/set differently every so many months?


texts: What can we expect from the first accurate image of a black hole?

texts:
From recent news from the Max Planck Institute for Radio Astronomy:

  The European Research Council (ERC) has awarded 14 Million Euros to a
  team of European astrophysicists to construct the first accurate image
  of a black hole. The team will test the predictions of current
  theories of gravity, including Einstein's theory of General
  Relativity.

I've seen computer depictions of black holes in the past, are they similiar to what we can expect from this new endeavour?

In the next image we can see a computer model of a black hole of ten solar masses as seen from a distance of 600km with the Milky Way in the background with a horizontal camera opening angle of 90 degrees:

Image Source


texts: How much dimmer is a partial solar eclipse that goes from -26.71 to -25.89?

texts:
Based on what I found in Stellarium, for Vlissingen, Netherlands, on July 2, 1666 there was a partial eclipse with a change of apparent brightness -26.71 to -25.89.
Is it valid to say based on the chart below that the sun would've appeared a little more than 50% dimmer at maximum compared to before the eclipse?
If not, approximately how much dimmer was the sun during this eclipse, based on the values given by Stellarium?

Source

above: Just before the start of the eclipse. below: At maximum


texts: Can we draw a min(distance) and max(mass) relation based on current observation data of nearby astronomical objects within several parcsecs?

texts:
The data precision now can exclude a >>$1M_{\odot}$ black hole companion, which has a, say 10000 year orbital period with our sun?

Can we draw a two dimensional diagram(Mass VS. distance) to show the region that is still a grey area? Within 1 pc, there is no stellar mass black hole? If there is one, the orbit change of objects in solar system may be detectable.

How to calculate its proper motion or its planets' proper motion?

I am serious to ask. Please give some reference/technical method to calculate PM. For example, is there some reference paper about the distance limitation of the black hole based on the motion of asteroids/comets?


texts:
I have seen the term superficial gravity used and it seems to be equivalent to surface gravity

seen, e.g., here http://arxiv.org/pdf/1701.02295

Is there any difference between superficial and surface gravity? When should one be using one or the other?


texts: Is it possible that Mercury was originally the moon of Venus after a giant impact?

texts: Mercury looks like the Moon, and so it makes me think about a question: is it possible that Venus and Mercury were the a same planet originally, and a giant impact with that planet made it split into Mercury and Venus (like with the Moon and Earth)?


texts: Does the perceived colour of the sun change based on the observer's location?

texts: A friend of mine visited Panama and claimed the sun appeared whiter. He's very color conscience and says certain shades of red looked different there. Could this be due to the position of the sun?


texts: What types of signals is SETI (and other such efforts) looking for?

texts:
This seemed to be the closest group for this question.

Every few months there are a few articles asking "Are we alone in the universe" which focus on the Fermi Paradox, the Drake Equation, and end by talking about SETI and its lack of progress. As I understand it SETI is looking for signs of technological civilizations beyond our solar system, both in our galaxy and beyond through radio astronomy.

My question is about what would count as a "sign" of a technological civilization, and is there a maximum distance beyond which such a signal would be indistinguishable from other radio emissions from stars and galaxies?


texts: What does a solar eclipse at 99% totality look like?

texts: People smarter than me say the sun will be 99% covered during the 2017 solar eclipse where I live (Portland, OR metro). I am curious to know what it might look like (photo or drawing). Does this photo approximate 99% coverage? Or will there be slightly more sun? Will I still see some of the corona?


texts: How do I calculate moon phase orientation at any Coordinates given all the necessary data?

texts:
I'm having a problem for a couple of days where I'm trying to accurately calculate the phase angle of the moon at any given Coordinates (lon,lat).If I know my current Coordinates, Moon and sun topocentric right ascension, declination, altitude and zenith Coordinates.

Given all of that data, how do I achieve that ? The result I'm looking for preferable in degrees where 0 degrees means the crescent moon pointing directly towards me, 180 degrees means the crescent moon pointing at the other direction and so on..

I have tried a formula where I measured the angle between the sun zenith and a certain coordinate in relation to the moon zenith, on paper this could work, the results were decent but not to the accuracy I'm looking for. Any help would be much appreciated.


texts: How massive does a planet need to be to create gravitational lensing?

texts:
Is it ever possible for starlight to be distorted in a noticeable way from something as small as a planet?

I'm guessing that the chances of this working are better on a dense terrestrial planet than a gas giant.

How do you calculate this?

Edit: I was unclear, sorry. I'm specifically thinking about lensing that would distort the shape of a star, not just move its position.


texts: Calculate planet's surface temperature by distance from star

texts:
If the planet and star in question are very similar to the Earth and the Sun, how can I calculate the planet's surface temperature by knowing the distance from the star?

This question was originally asked on the Worldbuilding stack exchange, and someone suggested I ask it here.


texts: Is it possible that in the Local Interstellar Cloud there are undetected stars?

texts: The Local Interstellar Cloud is supposed to be around 30 light years large. Is it possible that in this region there are stars which are undetected? I would have thought that it wasn't possible, but there are stars which are very small or are very close to another star. BTW, with star I mean an astronomical object which is performing fusion, because I've seen lists of smallest or coldest stars which includes brown dwarfs which don't perform fusion or white dwarfs.


texts: How does gradual crossing over of the Roche limit transform a planet or moon?

texts:
Some cartoon simulations (an example) of an object (assume here a large moon with Earth-like density) which crosses the Roche limit of a much more massive giant planet, illustrate a circle suddenly disintegrating and forming a ring. But such a process occurs gradually over geological time scales. I doubt that there would be a single bad day when the whole moon disintegrates (as in -Oh, there Mt. Everest broke off and flew away!)

Wouldn't the tidal tugging cause volcanism and gradually melt the moon as its (somewhat eccentric) orbit spirals inwards across the limit during millions of years?

How would the melting moon deform? Would it really assume an oval shape, elongated towards the primary planet? Since the near side wants to orbit faster than the far side, wouldn't that cause the moon to spin at an accelerated rate, even if it initially was tidally locked? Would the melting, deforming and spinning save it from disintegrating further to within the Roche limit?

Some examples of Roche limit crossings I know of:

Comet Shoemaker-Levy 9 may have broken up suddenly because it had
such a high velocity relative to Jupiter.
Phobos will cross its Roche limit to Mars in ~50 million years. It
will hardly be a sudden process. I suppose its very low density and
mass won't allow any volcanism and melting, though.
KOI1843.03, an exoplanet candidate with a density of ~7 g/cm³,
is already inside the Roche limits for its less dense compounds which
it has shed (as I interpret it).


texts: Speed of Moonrise relative to fixed point on ground

texts:
Due to the curvature of the earth, and the way the moon interacts with the atmosphere (especially close to the horizon), is there a known function that describes the speed of the moon relative to its angle in the sky?

For bonus points, imagine that you are at altitude in a plane, and for some reason want to descend at a rate that would keep the total % of the moon illuminated constant. Is there a function for that?

Thank you in advance, this is not for an assignment, just for my own curiosity as I watched moonrise tonight. I have tried googling these questions, to no avail.


texts:
How many black holes exist and what is their distrubtion over mass?
There is a list of black holes, but I'm interested in an estimate of all black holes in the visible universe.


texts: Let say that the Earth's Moon was knocked out of orbit and landed on the Earth with some damage but not world ending. Would Earth's atmosphere envelop to include the Moon? Would the moon sink into the Earth? What would happen?


texts: How can we map masses orbiting the outer Solar System by determining the orbits of planets and smaller objects?

texts:
Neptune was discovered 170 years ago with the help of observations of Uranus' orbit. A great demonstration of the scientific principle for its time. Recently, Earth and cis-Lunar based radio interferometry together with the Cassini orbiter have measured Saturn's orbit, 10 AU from the Sun, with very great precision. This has already helped determine some characteristics of a possible planet Nein 200-700 AU from here.

What would be the best way to gravitationally measure the yet unobserved mass concentrations in the Kuiper Belt and beyond, by observing orbits of objects among the known planets?

It takes alot to move Saturn to a measurable degree. What about a space probe with the sole purpose of being easy to locate at high precision, maybe in a highly inclined orbit? Or a family of them in different directions. Would its deplacement from the very weak gravity well of a planet Nine be detectable? If it is the history of Saturn that contributes crucially to the precision, what about an asteroid like Ceres which is known since 200+ years? Is there any special property of Saturn that makes it especially useful? Would a second object as well measured as Saturn be extra helpful by some kind of triangulation of distant gravitational influences?


texts:
I have telescope with a diameter of 60 mm and a focal length of 900 mm. I have a 2x Barlow lens and eyepieces with focal lengths of 10 mm. Can I see any details of any galaxies? Andromeda for an example? What galaxy is the best for watching with this small telescope? I have f15.
I can view one galaxy but I don't know what exactly. It looks really small with no details.

What do you suggest I try to find in the sky? I viewed Saturn and I was delighted.


texts: How to trim CCD overscan and amplifier turn on/off regions

texts:
I have begun reducing images I collected with a telescope and CCD detector. I read in the the "Handbook of CCD Astronomy" by Howell that I need to trim overscan regions (as well as possible amplifier turn on/off) regions before I can compute the gain of the detector. However, it is not thoroughly clear where this boundary is.

If we treat the CCD detector as a matrix of pixels, then I know that the overscan region is along the edge columns. To visualize this, I computed the average and standard deviation along each column of pixels to view the variation in intensity from column to column. Below I inserted the left side of two amplifier matrices on my CCD detector:

The blue is the column-wise average and the green is the column-wise standard deviation. The y-axis is the (arbitrarily scaled) intensity and the x-axis is the pixel distance from the edge of the CCD array.

My question is essentially: how much of the blue and green curve should I cut-off?

Edit: additionally, it should be noted that I am using the method outlined in "CCD Data..." by Massey & Jacoby (1992) link to compute the gain.


texts: What is difference between horizon and comoving distances?

texts:
I wonder if there a difference between horizon and comoving distances in cosmology ?

I mean both correspond to a null geodesic $(ds^2=0)$ right ?

$$d_{horizon} (t) =a(t) \int\limits_{0}^{r} \frac{{\rm d}r'}{\sqrt{1-kr'^2}}= a(t) \int\limits_{0}^{t}\frac{ c \, {\rm d}t'}{a(t')}$$

with $a(t)$ the scale factor.

Is the difference just that for a comoving distance the integration bounderies changes ? like $r_e$,  $r_0$  and $t_0$, $t_e$

Thanks in advance for help


texts: Today I was wondering with a friend about the birth of a star. So we know that stars are born from a nebula, but the residue of a dead star (like a supernova) is itself a nebula. So can a star be born from this nebula?


texts: Accurate catalogue of the Stars according to Hemisphere

texts:
I am in the need for an accurate catalogue of the stars in the Hemisphere I am currently in (or the one that I chose) and their positions at any time of the year.
The more accurate the catalogue is, the better. I don't want any live-time-location app, but a simple place whence I can refer where a star or any other celestial object is.
What do you mean by a 'live-time-location app'?
To answer this question asked by @DrChuck in the comments below, I will take the example of an Android app called 'Skymap'. This app takes your live location and uses the phone's internal compass to determine what direction the phone is pointed in, and shows the celestial objects (visible/non-visible) in the direction according to the time-settings of your phone.
What data are you looking for?
Another question asked by @DrChuck in the comments below. I am looking for the following info :-

Catalogue of all stars visible from all over the Hemisphere.
Their respective positions.
Catalogue of other celestial objects like Galaxies, etc.
Special events like Solar Eclipses visible from the Hemisphere.*
Position of any celestial body during any time in the future or past.*
(*  - Not necessary)

Um, can we make things, well, simpler?
Some things listed below are really not necessary :-

It does not matter if it does not list the objects that cannot be seen through the naked eye.
It does not have to be really complicated. Anything a normal person can use is fine.

P.S. - Any help with any appropriate tags for this question will also be appreciated.


texts: What's the fastest moving object in the universe?

texts: We know that nothing can have proper velocities larger than the speed of light in vacuum. But are there any objects in space that get close to it? Any comets, or other objects thrown by gravity or supernova explosions that were hurled to incredible speeds?